The silane coupling agent was originally developed as a glass fiber reinforced plastic glass fiber treatment agent. Since the silane coupling agent improves the adhesion between the glass fiber and the resin, the mechanical properties of the reinforced plastic are remarkably improved. With the rapid development of composite materials, silane coupling agents are developing at a rapid rate regardless of variety or yield. In recent years, the use of silane coupling agents to introduce specific functional groups to certain materials can improve the surface properties of materials, obtain anti-static, anti-mildew, anti-odor, anti-coagulation and physiological inertness, etc., and become a new use of silane coupling agents. beginning. It is precisely because of the development of many important application areas that silane coupling agents have become an important branch of silicones.
The silane coupling agent is obtained by adding chloroform (HSiCl3) and an unsaturated olefin having a reactive group under the catalysis of platinum chloric acid, followed by alcoholysis. The silane coupling agent is essentially a type of silane having an organic functional group, and has a reactive group capable of chemically bonding with an inorganic material (such as glass, silica sand, metal, etc.) and an organic material (synthetic resin, etc.) in the molecule. Chemically bonded reactive groups. It can be represented by the general formula Y(CH2) nSiX3, where n = 0 to 3; an X-hydrolyzable group; and an Y-organic functional group capable of reacting with a resin. X is usually a chloro group, a methoxy group, an ethoxy group, a methoxyethoxy group, an acetoxy group, etc., and these groups form a silanol (Si(OH)3) upon hydrolysis, and combine with an inorganic substance to form Silicone. Y is a vinyl group, an amino group, an epoxy group, a methacryloxy group, a decyl group or a ureido group. These reactive groups can be combined with an organic substance to react.
Therefore, by using a silane coupling agent, a "molecular bridge" can be built between the interface between the inorganic substance and the organic substance, and the two materials with different properties can be connected together to improve the performance of the composite material and increase the bonding strength. . This property of silane coupling agent was first applied to glass fiber reinforced plastic (glass reinforced plastic) as a surface treatment agent for glass fiber, which greatly improved the mechanical properties, electrical properties and anti-aging properties of FRP, in the FRP industry. The importance has long been recognized.
Currently, the use of silane coupling agents has expanded from glass fiber reinforced plastic (FRP) to glass fiber surface treatment agents for glass fiber reinforced thermoplastics (FRTP), surface treatment agents for inorganic fillers, and sealants, resin concrete, and water. Crosslinkable polyethylene, resin encapsulating materials, shell molding, tires, belts, coatings, adhesives, abrasives (grinding stones) and other surface treatment agents.
Among the two groups of silane coupling agents with different properties, the Y group is the most important, and it has a great influence on the properties of the product, which determines the performance of the coupling agent. The strength of the composite can only be increased when the Y group reacts with the corresponding resin. It is generally required that the Y group be compatible with the resin and capable of undergoing a coupling reaction. Therefore, a certain resin is selected to contain a silane coupling agent having an appropriate Y group. When Y is an unreactive alkyl or aryl group, it is ineffective for polar resins, but can be used for bonding of non-polar resins such as silicone rubber, polystyrene, and the like. When Y contains a reactive functional group, attention should be paid to its reactivity and compatibility with the resin used. When Y contains an amino group, it is catalytic, can be used as a catalyst in the polymerization of phenolic, urea-formaldehyde, melamine formaldehyde, and also as a curing agent for epoxy and polyurethane resins. At this time, the coupling agent is completely involved in the reaction to form a new bond. . Aminosilane-based coupling agents are of a general-purpose type and can be coupled to various resins, except for polyester resins. The type of x group has no effect on the coupling effect.
Therefore, depending on the kind of the reactive group in the Y group, the silane coupling agents are also referred to as vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloxy silane, respectively. It is the most commonly used silane coupling agent.
The application of silane coupling agents can be roughly summarized into three aspects:
(1) It is used for the surface treatment of glass fiber, which can improve the bonding performance of glass fiber and resin, and greatly improve the strength, electrical, water resistance and weather resistance of glass fiber reinforced composite materials, even in the wet state, it is The mechanical properties of the composite material are improved and the effect is also remarkable.
At present, the use of silane coupling agents in glass fibers has become quite common. The silane coupling agent used in this aspect accounts for about 50% of the total consumption, and the most used varieties are vinyl silane, amino silane, Methacryloxysilane or the like.
(2) Used for filling inorganic fillers with plastics. The filler may be surface treated in advance or added directly to the resin. It can improve the dispersibility and adhesion of the filler in the resin, improve the process performance and improve the mechanical, electrical and weather resistance properties of the filled plastics (including rubber).
(3) Used as a tackifier for sealants, adhesives and coatings to improve their bonding strength, water resistance and weather resistance. Silane coupling agents often solve the problem that certain materials have not been able to bond for a long time.
The principle of the silane coupling agent as a tackifier is that it has two groups by itself; one group can be bonded to the bonded matrix material; and the other group can be combined with a polymer material or a binder. Thus, a strong chemical bond is formed at the bonding interface, which greatly improves the bonding strength. There are generally three methods for the application of the silane coupling agent: one is a surface treatment agent as a skeleton material; the other is added to the binder, and the third is directly added to the polymer material. The first two methods are better from the perspective of giving full play to their effectiveness and reducing costs.